Magnetron



Jan-l 1958 J. FEINSTEIN 2,821,659

MAGNETRON Filed Nov. 18, 1954 INVENTOR J. FE/NSTE/N OLMDF A ATTORNEYUnited States Patent MAGNETRON Joseph Feinstein, Morristown, N. 1.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York Application November 18, 1954, Serial No.469,644

18 Claims. (Cl. 315-3957) This invention relates to electron dischargedevices and more particularly to multicavity magnetrons.

When oscillations start to build up in a resonant circuit comprising aring of cavity resonators, such as in a multicavity magnetron,competition exists between the various possible modes of oscillation.Generally it is desired to have oscillation occur in what is referred toas the rr-mode. However, under various conditions the build-up ofoscillation in a different mode may be preferred by the circuit; thisbuild-up of oscillation in other than the desired 1r-m0d6 of oscillationis referred to as moding. The usual approach to the moding problem hasbeen two-fold: mode frequency separation and selective mode loading. Thefrequencies of the modes of the magnetron resonator system near that ofthe 1r-mode would ordinarily be closely grouped were not steps taken toseparate them. Priorly mode separation has generally been accomplishedby two methods. The first, and more common, has been to increase thecoupling by conductive connections between the resonators andparticularly by employing straps; this is generally referred to asstrapping. This increases the frequency separation by increasing thecoupling between resonators. The second method has been to use cavitiestuned alternately to different frequencies; this latter method has beenemployed in what is generally referred to as the rising-sun anodestructure. This method increases the frequency separa tion by detuningthe adjacent resonators relative to one another.

Further to prevent moding, selective loading of the degenerate orunwanted mode most likely to oscillate in place of the 1r-mode has alsobeen employed. This mode is generally the one closest in frequency tothe 1r-mode. Selective loading may be obtained by changes in theinternal anode structure of the magnetron or by elements locatedexternal to the magnetron and particularly in the output wave guideconnected to the magnetron.

These prior methods have not generally proven satisfactory at higherfrequencies. Strapping is limited in the number of resonators that maybe employed. Further the two approaches of frequency separation and modeloading are not independent of each other, the selective loading in facttending to hinder the mode separation. At high frequencies this has beenfound to raise serious problems in prior structures.

It is a general object of this invention to provide improved anodestructures for multicavity magnetrons.

Further objects of this invention include improving the frequencyseparation of the mode of oscillations of a magnetron, enabling improvedoperation of magnetrons at high frequencies, and preventing moding inmagnetrons when operated at high frequencies.

As mentioned above, the mode separation in a magnetron can be varied asthe coupling between adjacent resonant cavities is varied. In accordancewith one aspect of this invention, optimum coupling between adjacentresonators is attained not by conductive connections,

ice

such as straps, but by a capacitive coupling adjacent the inductiveregions of the resonators.

In one specific illustrative embodiment of this invention a magnetroncomprises a plurality of hollow anode segments mounted circumferentiallyaround the central or cathode cavity. Advantageously the anode segmentsmay be formed as hollow vanes as by the forming or bending of a metalstrip. At the base of each vane are a pair of capacitance membersextending inwardly toward each other and defining a small capacitivegap. The vanes may advantageously be supported from an outer anode rimby T-shaped members which provide the end closure for the resonatorslots defined between adjacent anode segments. Two adjacent T-shapedmembers also define a capacitive gap, of slightly larger dimensions,directly adjacent, and electrically in parallel with the first gap. Thetwo T-shaped members thus also enclose a hollow portion.

For the 1r-mode of oscillation, there is no potential across thesecapacitive gaps and therefore no 1r-Il'l0d6 energy is stored in thesegaps. For other modes of oscillation, however, a potential difierencedoes exist across the gaps and energy of these modes is stored; theoptimum condition for mode separation is that one half of the energy ofthe unwanted modes is stored in the capacitance gaps, the other halfbeing stored in the capacitance of the resonators itself.

In order to utilize the potential difference between these two pointsdefining the capacitance gap at the base of each anode vane, it isnecessary that this coupling capacitance not be shorted by the anodevane or segment itself. Accordingly, each anode segment is made hollowto serve as a choke and prevent the continuous conducting path of theanode segment providing an electrical short across the gap. As the areaof the anode vane is limited, the choke defined by the hollow vane alsois limited; accordingly, it is advisable to have the gap across the baseof the anode vane small to have a high capacitance so that the chokesection may be also quite small. The inductances of these choke sectionsshould be sufficiently great that they have a negligible shunting effecton the capacitance gaps at the frequencies of the magnetron. Thus thehigh capacitance, low impedance gap is advantageously employed with thesmall choke section possible in the anode vane.

However, in accordance with another aspect of the invention, additionalenergy of the unwanted mode fields is stored in the capacitance gapdefined between the ends of adjacent T-shaped sections supporting theanode vanes. As noted above, these second gaps are directly adjacent andin parallel with the primary gaps at the base of the anode vanes. Asecond choke section is also provided for these gaps; this choke sectionis advantageously defined by the hollow portion bounded by two adjacentT-shaped members and the outer supporting rim. In this case there is nolimitation necessarily imposed on the area of this choke section, as thediameter of the outer rim and the length of the T-shaped members may beincreased as desired. It is thus possible to have these secondary gapsof low capacitance values for the storage of the field energy of theunwanted modes.

As only the unwanted mode energy is stored in these gaps, loading of theunwanted modes can readily be attained, in accordance with anotherspecific embodiment of this invention, by introducing a lossy dielectricinto these gaps. This can be a material, such as barium titanate, whichcan introduce loss to reduce the Q of the unwanted modes. The insertionof a lossy dielectric material possessing a loss factor tangent 9 inthese capacitors has a first order effect of reducing the Q of theunwanted modes to 1/ tan 6. There is actually also a second order 3effect tending to reduce the mode separation, but this remainsnegligible until loss factors of the order umty are reached.

It -is a feature-of this invention that an anodeyfor employment in amagnetroncompriseaplurality of-hollow anode segmentshavingcapacitancememoers at the base of the anode extending across the hollow portion anddefining a capacitance gap.

It is a further feature of this-invention that the anode segments besupported by conductive members defining a second capacitance gapdirectly-adjacent and parallel to each of the firstgaps, the conductivemembers also defining a hollow choke portion communicating with thesecond gap.

It is another feature of certain embodiments of this invention that-alossy dielectric material be inserted into the capacitance gaps thusdefined in the anode structure. I

It is a still further feature of "this invention thata magnetroncomprise hollow anode segments having capacitance gaps across the basethereof for the storage of energy of the unwanted modes of oscillation,the hollow portions serving as choke sections to prevent the shorting ofthe capacitance gaps by the anode segments themselves.

A complete understanding of this invention and of the various featuresthereof may be gained from consideration or" the followingdetaileddescription and the accompanying drawing, in which:

Fig. 1 is a sectional view of a'magnetron illustrative of one specificembodiment of this invention;

Fig. 2 is aplan view of the anode and cathode structures of theembodiment of Fig. 1 taken along the line 22 thereof; and

Fig. 3 is a partial plarrview of an anode structure in accordance withanother specific illustrative embodiment of this invention.

Referring now to the drawing, the specific illustrative embodiment ofthis invention depicted in Fig. 1 comprises an anode structure :10, bestseen in Fig. 2, mounted by a circular rim member 11 between the two polepieces 12 and 13. A cathode sleeve 15 extends through the centralaperture of: the anode it) and has coated thereon an electron emissivecoating between apair of magnetic collars 17. A heater element 19extends within the cathode sleeve 15 and is connected to a pair of leads20. One lead :20 is connected to an inner cylindrical terminal conductor'21 and the other to an outer cylindrical terminal conductor 22, the twoterminals and 22 being insulated K The output resonator 32 of the anodestructure is 'conected, through a dumbbell or basically H-shapedtransformer section 33, as is known in the art, to an output Wave guidesection 35' through which the energy of the magnetron is transmitted toexternal circuitry. The output wave guide section 35 serves as animpedance transformer between the output of the magnetron and theexternal circuitry and has hermetically sealedthereto a window 36transparent to the passage of microwave energy.

Heat radiating vanes 38 are advantageously supported 'by a metallicbodymember 39 in which is also located the dum beil shaped wave guideoutput section 33. An xhatisttubul'ation 49 is secured toa side aperturein the pole piece 13-to enable the exhausting of the magnetron.

In this specific embodiment ofthe invention, the anode structure 10.as-seen in Figu2, comprises a. pluralityof hollow anode vanes or=segments 45 ='which may advantageously be each 'formed'of a single stripof a conducting material; each anode vane encompasses a hollow chokesection 4'6. 'At'thebase of eachva'ne ts and astending inwardly acrossthe hollow section 46 are a pair of capacitance gap defining members 47;members 47 thus define a plurality of capacitance gaps 48 which serve tocouple capacitively adjacent resonator slots 49 defined between adjacent*anode' vanes 45.

The resonator slots-49--are-open adjacent the central cavity of theanode, in which cavity the cathode sleeve 1. S 'is located, and:are-e'ach closed at their other "end'bya T-shaped-support 'member SLSecured to ac'h'-'cross or T-section of members 51 are one side ofeachof two adjacent anode vanes 45-and theone capacitance member 47connected to each side. Between adjacent cross or T-sections ofmembers-5'1thereisthus defined a second capacitance gap 53, which gap isdirectly adjacent and electrically parallel to the primary gaps 48defined by members47 secured to the base of the anode vanes 45.

A hollowchokesection 54 is defined between adjacent T-shaped membersfilby the adjacent members'o'l and thesupportingcircular rim member 11. Theindividual anode vanes 45 are thus each supported bytwo T-shaped members51 which'in turn are secured to the outer rim member 11.

ln-accordance with anaspect of this invention, mode separation isattained by the capacitive coupling 'between adjacent resonators "49afforded by the capacitive-gaps 4-8-and 53 and specifically by thestorage of field energy of unwanted modes in these gaps. Th hollowsections 46 and 54 define inductance chokes which prevent thecapacitance, gaps from being shorted by the conducting paths of tlieanodevanean'd support members, respectively. 'As the hollow section' lfiwithin the anode vane 45 is limited in area, the capacitance. gap 48 isadvantageously of a 'sufficiently small sizeso that the choke sectioncan adequately assure that the conducting path ofthe vaneha's anegligible shunting effect on the capacitance 'ga'p48 associatedwith'the vane. The hollow sections 54, however, "may'be formed ofsubstantially any desired size by; increasing the diameter of the-outercircular'rim 1'1 'a'nd'the length of the upright portions of'theT-shaped memberssl. Capacitance gaps 53 accordingly maya'dva'ritage'ously'be-larger than the primary cap'acitance'g'aps 48.

The modeseparation'in'the anode-structureof'Fig. 2 is attained'by thiscapacitive coupling between adjacent resonators 49 and essentiallyacross the base of each anode segment. The inductive'ch'okes formed bythe hollow sections 46 within theanodc vanes 45 themselvespreventshorting'of the'capacitancesthus formed 'bet'we'en'the two parts of the'anod'ese'gments"45. Andthe'supporting members 51-forthe"anodevanes'provide'both additional coupling capacitance and another chokesection to enable storageofmore energy'of the unwanted modes.

As there is now-mode potential betweenadjacent resonators'and thusthereis only'field energy of the unwanted modes storedinthe couplingcapacitances defined by gaps 48 and 53, the unwanted'modes ma'y'readily'be loaded by inserting a lossydielectric into'these gaps. In thespecific illustrative "embodiment depicted in Fig. 3, this has beendo'ne. Advantageously the lossydielec'tric 56, which'may be'of bariumtitanate'or other dielectric material having a high lossfactor, issecured directly to the gap definingme'mbersythis may'bc'done 'byplating a thin layer-of silver onto thQSlClQSCftlle dielectric material56 and silver b'ra'zing the silver plated dielectric material to'the'sides ofthe gap defining members.

lt is to be understood that the above-described arrangem'ents'are'illustrative of the application of the principles of the invention.Numerous-other arrangementsmay be devised by th'ose'skilledin thea'rtwithout departing from the-spirit and scope of the invention.

l. A ina'gfietr'oncomprisinga plurality of "anodesegine'nts definingresonant cavities between adjacent segments, said segments having hollowportions therein, and capacitance members at the base of said segmentsacross said hollow portions and defining capacitance gaps for thestorage of energy of unwanted modes of oscillation, said hollow portionsserving as choke sections to prevent the shorting of said capacitancegaps by the anode segments.

2. An anode for employment in magnetrons comprising a plurality of anodesegments defining resonant cavities between adjacent segments, saidsegments having hollow portions therein, capacitance members at the baseof said segments across said hollow portions and defining capacitancegaps, and means supporting said anode segments.

3. An anode in accordance with claim 2 wherein said supporting meanscomprises conductive means defining second capacitance gaps positionedadjacent said firstmentioned gaps, said conductive means having hollowportions communicating with said second capacitance gaps.

4. An anode in accordance with claim 3 wherein said second capacitancegaps are longer than said first-mentioned capacitance gaps.

5. An anode for employment in magnetrons comprising a plurality of anodesegments defining resonant cavities between adjacent segments, saidsegments having hollow portions therein, capacitance members at the baseof said members extending inwardly across said hollow portions anddefining capacitance gaps, means supporting said anode segments, andlossy dielectric elements positioned in said gaps.

6. A magnetron comprising a cathode, a plurality of anode segmentsencompassing said cathode, said anode segments defining resonantcavities between adjacent segments and said segments having hollowportions therein, capacitance members at the base of said segments andextending inwardly across said hollow portions, the capacitance membersof each segment defining a capacitance gap for storage of energy ofunwanted modes of oscillation of the magnetron and the impedances ofsaid gaps and said hollow portions being such that said gaps are notappreciably shunted by said anode segments, and means supporting saidanode segments.

7. A magnetron in accordance with claim 6 comprising lossy dielectricelements positioned in said gaps to load the unwanted modes ofoscillation of the magnetron.

8. A magnetron in accordance with claim 6 wherein said supporting meanscomprises conductive means defining second capacitance gaps positionedadjacent said firstmentioned gaps, said conductive means having hollowportions communicating with said second gaps and the impedances of saidsecond gaps and said second-mentioned hollow portions being such thatsaid second gaps are not appreciably shunted by said conductive means.

9. A magnetron in accordance with claim 8 comprising lossy dielectricelements positioned in said gaps to load the unwanted modes ofoscillation of the magnetron.

10. A magnetron comprising a cathode, a plurality of anode segmentsencompassing said cathode and defining resonant cavities betweenadjacent anode segments, means including portions of said segmentsdefining a capacitance gap between each two adjacent resonant cavities,and means supporting said anode segments, said supporting meansincluding conductive means defining a second gap between adjacentresonant cavities.

11. A magnetron comprising a cathode, a plurality of anode segmentsencompassing said cathode and defining resonant cavities betweenadjacent anode segments, means including portions of said segmentsdefining a capacitance gap between each two adjacent resonant cavities,means supporting said anode segments, and lossy dielectric elementspositioned in said gaps.

12. A conductive circuit element comprising a plurality of hollowconductive members, means mounting said conductive memberscircumferentially, adjacent ones of said conductive members definingresonant cavities, and a pair of conductive elements mounted on each ofsaid hollow conductive members external of said resonant cavities andextending inwardly across the hollow thereof, said conductive membersdefining capacitance gaps between adjacent ones of said resonantcavities.

13. A conductive circuit element in accordance with claim 12 comprisinglossy dielectric elements positioned in said gaps.

14. A conductive circuit element in accordance with claim 12 whereinsaid mounting means comprises means defining second capacitance gaps andhaving apertures therein communicating with said second gaps.

15. A conductive circuit element in accordance with claim 14 comprisinglossy dielectric elements positioned in said priorly mentioned and saidsecond gaps.

16. A conductive circuit element in accordance with claim 14 whereinsaid second gaps are larger than said priorly mentioned gaps and saidapertures are larger than the 'hollow defined by said conductivemembers.

17. A conductive circuit element comprising a plurality of thin vanesegments, means mounting said segments circumferentially, adjacent onesof said segments defining resonant cavities therebetween, and a pair ofconductive members mounted on each of said vanes at the base thereof andextending inwardly of each segment, each pair of conductive membersdefining a capacitance gap across the base of each segment.

18. A conductive circuit element in accordance with claim 17 whereinsaid mounting means comprises means defining a second capacitance gapadjacent each of said priorly mentioned gaps and communicating therewithand having an aperture therein adjacent each of said second gaps andcommunicating therewith.

References Cited in the file of this patent UNITED STATES PATENTS2,480,126 Frankel "um-"n-.." Aug. 30, 1949

